1. Field of the Invention
The invention concerns gas cooled high temperature reactors having a cylindrical steel pressure vessel, heat exchanger devices, cooling gas circulation devices and circulating blowers.
2. Background of the Prior Art
The state-of-the-art includes installations wherein a high temperature reactor for the nuclear generation of heat and the devices serving the utilization of the heat obtained are installed together in a pressure vessel. The heat is removed by means of a cooling gas which is being circulated with the aid of blowers in a closed loop or primary loop through the reactor core and the heat exchanger devices. For the removal of the residual heat, special devices, such as auxiliary heat exchangers and auxiliary blowers are often provided It is also possible to eliminate these special devices by means of a particular arrangement and layout of the primary loop components.
Thus for example in the thorium high temperature reactor (THTR-300), the heat exchangers and the blowers together with the pipe circuits on the secondary side and their components are laid out so that the entire secondary heat is removed by means of the operating systems of the heat exchangers on the primary side The flow of the cooling gas from top to bottom through the reactor core and from bottom to top through the heat exchangers in this case is similar to that in normal operation. To assure the removal of secondary heat, however, the blowers must at all times be ready to function so that the area of the cold gas will not be endangered by the hot gas rising in free convection.
In a further nuclear reactor installation with a gas cooled high temperature reactor, the so-called AVR plant, the heat exchanger is arranged above the nuclear reactor and the cooling gas flows from bottom to top both through the reactor core and through the heat exchanger. In the event of a failure of the blower located underneath the core, the residual heat is removed by natural convection to the structures surrounding the reactor core. The latter include in addition to a reflector jacket of graphite, a carbon brick enclosure surrounding the graphite jacket and providing shielding and thermal insulation. To safely contain the fission products released, the aforementioned structures are surrounded by a double, gas-tight steel pressure vessel. A layer of magnetite and limonite between the two steel pressure vessels serves as a biological shield.
In the above mentioned THTR-300 the function of the biological shield is effected by the prestressed concrete pressure vessel, which houses in a centercavity, the reactor core and the heat exchangers. The prestressed concrete pressure vessel not only serves as the radiation shield, but also provides a complete, pressure resistant containment of the nuclear reactor installation.